Electrodeposition of tin-antimonycopper alloys



ELECTRODEPOSITION F TIN-ANTIMONY- COPPER ALLOYS Quentin 0. Shockley,Indianapolis, Ind., assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware No Drawing. Application December 11,Serial No. 261,153

8 Claims. (Cl. 204 --44) The present invention relates to a method andbath for alloy electroplating and is more particularlyconcerned with theelectroplating of alloys containing tin,fcopper and antimony.

Alloys of tin, copper and antimony, andmore particu.

ularly the tin base alloys containing copper and antimony, have longbeen accepted as satisfactory bearing materials. However, to preparethese alloys it has always been necessary to cast them from the moltenstate. In accordance with my invention such alloys are electrodeposited,thus accomplishing considerablesimplification in manufacturing methodsand procedure; A hearing metal layer, for example, can be plated on toabacking metal and the thickness of the metal layer closely controlledso as to dispense with subsequent machining operations to remove excessmetal. Also, in many instances, a superior bearing surface can beobtained'by electroplating than can be accomplished by means of thecasting process.

It is an object of this invention to provide a new and useful method andbath for electroplating alloys of tin, copper and antimony. Otherobjects and advantages of my invention will be apparent in thefollowing'description of the preferred embodiments. 7

Briefly, my invention consists in plating tin-copperantimony alloys byelectrodeposition. from an aqueous bath containing the fluoborate saltsof these metals. Bath additives, such as betanaphthol and glue may beadded to the bath to improvethe quality of the plate. Variations in thecomposition of the alloy can be accomplished by variations in thecurrent density and in the anode'composition as Well as by variations inthe concentrations of l Grams per liter Tin from 60 to 80 Copper from 1to Antimony from 1 to 5 It is generally advantageous to add to the bathfrom .25 to 2 grams per liter glue, and to maintain thebath saturatedwith betanaphthol. At room temperature this amounts to approximately 1gram per liter of betanaph thol. The pH is maintained at'between 0 and1, and temperatures of from 70 to 100 F. may be used. The anode mayeither be pure tin or else an alloy of tin and copper, such as an alloycontaining about 95% tin and about 5 %copper.- I have used the cathodecurrent densities of from to 60 amperes per square foot in conjunctionwith this bath, depending upon the exact alloy composition desired.

From a bath having the above range of metal concentrations and usingcurrent densities and anode materials within the range set forth,smooth, dense alloy platings containing from 79 to 97% tin, from 2 to12% antimony and from 1 to'8% copper, may be plated. The

particularly useful bearing alloys, such as SAE 10, 11 and 12, fallWithin this range.

The following specific examples of baths and of plating conditions fromwithin the above range, together with the alloy compositions obtainedtherefrom, Will serve for purposes of illustration:

Example I Anode: Sn95 Cu5 Cathode current density: 30 amperes per squarefoot Bath:

Tin grams per liter Copper do 1.0 Antimony do- 1.0 Boric acid do 20 Gluedo 1.0 Betanaphthol do 1.0 pH 0.3 Temperature F- 75 Agitation: Revolvinganode Deposit: Cu1.5%, Sb1.5%, Sn-balance.

Example ll Anode: Sn%, Cu-5% Cathode current density: 60 amperes persquare foot Bath:

Tin grams per liter 62 Copper do 3.5 Antimony do 4.5 Boric acid do 25Glue do 1.0 Betanaphthol do 1.0 7 pH 0.3 Temperature F 75 Agitation:Revolving anode Deposit: Cu-2.6%, Sb--7.7%, Sn--balance.

Example III Anode: Sn-95%, Ctr-5% Cathode current density: 60 amperesper square foot Bath:

Agitation: Revolving anode Deposit: Cu6.3%, Sb5.1%, Snbalance.

Example IV Anode: 100% Sn Cathode current density: 60 amperes per squarefoot Bath:

Tin grams per liter 75 Copper do 1.5 Antimony do 1.5 Boric acid do 20Glue do 1.0 Betanaphthol do 1.0 pH 0.3 Temperature F 75 Agitation:Revolving anode Deposit: Cu-8.9%, Sb--1l.2%, Snbalance.

Example V Anode: 100% Sn Cathode current density: 30 amperes per squarefoot Bath:

Tin ..grams per Men. 75 Copper do 1.5 Antimony do 3.5 Boric acid do 15Glue do .5 Betanaphthol do 1 pH 0.3 Temperature F 75 Agitation:Revolving anode Deposit: Cu--l.0%, Sb-6.l%, Snbalance.

For solution makeup and for concentration control I have found that atin fluoborate concentrate containing approximately 300 grams per literof stannous tin is satisfactory for addition of the tin constitutent.For addition of the copper constituent a copper fluoborate concentratecontaining approximately I80 grams per liter of copper can be used. Therequired antimony may be supplied in a number of ways. Antimonytrioxide, antimony trifluoride, potassium antimony tartrate, andantimony fiuoborate have all proved satisfactory. I have found that anantimony fiuoborate solution containing approximately 35% antimonyfiuoborate, 9% fluoboric acid, and .3% hydrofi'ouric acid, to be themost convenient source of the antimony addition. In all cases,irrespective of the type of addition solution used, it ha been foundbest to add the antimony compound as the last ingredient and after pHadjustment, since at this stage the antimony compound is most solubleand thus no difiiculty is had from precipitants.

To adjust. and maintain the pH, additions of a 42% commercial fiuoboricacid solution can be made. I have found it preferable to add about from10 to 40 grams per liter and preferably from to 25 grams per liter ofboric acid to the bath and then adjust and maintain the pH to thatdesired by additions of fiuoboric acid.

' The glue concentration is obtained by the addition of liquid glueobtained by dissolving bone glue pellets in a minimum amount of water.To maintain the solution saturated with'betanaphthol, an excessiveamount of this additivecan be stirred into the solution and, after aperiod ofagitatio'n, the undissolved material filtered out.

While I prefer to use an anode consisting of either pure tin or else ofan alloyof tin and copper, it is to. be understood, of course, that aninsoluble anode such as carbon or platinum may be used. The chiefadvantage of a tin or of a tin-copper alloy anode is that it assists inmaintaining the metal concentration of the solution. Anodes containingantimony have been found to be somewhat disadvantageous in that theysludge excessively.

It is generally preferable to agitate the bath solution during plating.This I accomplish by the use of a revolving anode; however, any suitableagitating means of course be used.

From the above listed examples it is apparent that differences inoperating conditions and differences in bath concentrations result invery significant variations in the deposited alloy. It has beenrecognized, for example, that variations in anode composition andposition have pronounced effect on the composition of the deposit. Forexample, using a bath having a composition of:

Tin grams per liter Copper 1.5 grams per liter Antimony 3.5 grams perliter Glue 1 gram per liter Betanaphthol Saturated solution (approx. 1

gram per liter) Temperature 75 F.

The following deposits were obtained under the conditions specified:

1. Rotating (approx. R. P. M.) internal anode Sn and 5% Cu) 60 amperesper square foot cathode current density. Deposit analysis: 5.5% Sb, 2.8%Cu, 91.7% Sn.

2. Stationary external anode (95% Sn and 5% Cu) and rotating cathode(approx. 80 R. P. M.) 60 amperes per square foot cathode currentdensity. Deposit analysis: 3.6% Sb, 2.3% Cu, 94.1% Sn.

3. Stationary external anode (pure Sn) and rotating cathode (approx. 80R. P. M.) 60 amperes per square foot cathode current density. Depositanalysis: 1.2% Sb, 1.5% Cu, 97.7% Sn.

The choice of location of the anode, that is, the choice of whether itis to be internal or external, will of course depend upon the' shape ofthe base metal being plated. Where, for example, the interior surface ofa bearing shell is to be plated, an internal anode is used. When anexternal anode such as a cylinder is used, then agitation can beaccomplished by the use of a revolving cathode, which is, of course, thearticle beingplated.

It will be apparent that under closely controlled conditions, varioususeful tin base tin-copper-antimony a1- loys within a wide range can beplated with our bath and process.

While the process and bath of my invention can be used, as above, toelectrodeposit Sn base alloys within the range of about 79 to 97% Sn, 2to 12% Sb, and l to 8% Cu, it can also be used to plate othertin-copperantimony alloys. A bath having metal ion concentrations withthe range of from 50 to 180 g./l. tin, from .5 to 20 g./l. copper andfrom .5 to 20 g./l. antimony, and containing fluoboric acid and boricacid and preferably glue and betan'aphthol within the ranges previouslyset forth, may be used. The current density can be from 10 to 60 amperesper square foot, the anode material being either pure tin, an alloy oftin and copper, or else an insoluble such as carbon or platinum. As inthe case of the previously mentioned baths, the temperature may be from70 to F. I have obtained alloys containing from 1.5% to 99% tin, from.4% to 15.5% antimony and from .2% to 98% copper with my process, theexact percentage composition depending, upon the various metal ionconcentrations in the bath and also upon the conditions used. Thefollowing table lists various plating baths and conditions along withthe alloy deposited therefrom:

containing from 50 to 180 g./l. tin as tin fluoborate, from .5 to 20g./l. antimony as antimony fluoborate, from .5

Anode Deposit Solution Ooficentratlon. current g. Cathode Composition fggg Type pgsmon per Antimony, Copper, Tin,

Tm copper Amt sq. ft. Percent Percent Percent P 7 Percent Percent TmCopper mony :32 s 2 .s 3-: as a 8 2 0. 100 90 10 10 35 0. 4 67. 2 Do.100 125 10 10 35 0. 7 60. 5 Do. 100 175 19 10 35 0. 7 97. 6 Do. 100 750. 5 0. 5 35 1. 1 0. 2 D0. 100 i 75 1. 5 1. 5 35 0. 7 1. 6 Do. 100 75 3.5 3. 5 35 7. 6 11. 9 D0. 100 75 0. 5 0.5 60 1. 1 0. 3 D0. 100 75 1. 5 1.5 60 0. 7 0. 9 D0. 100 75 3. 5 3. 5 60 11. 2 8. 9 D0. 100 75 10 10 6015. 5 29. 4 D0. 100 75 0. 5 0. 5 10 0. 4 2. D0. 95 75 1. 5 1. 5 0.6 4.0Do. 95 5 75 3. 5 3. 5 10 14. 6 23. 1 D0. 95 V 5 v 75 1. 5 3. 5 35 15.3 1. 3 D0. 95 5 75 1. 5 3. 5 35 15. 2 1. 5 Do. 95 5 75 1. 0 1. 0 60 0.5 1. 5 Do. 95 5 75 2. 5 2. 5 30 2. 9 9. 6 Do. 95 5 75 2. 5 2. 5 60 0. 74. 3 Do. 95 5 75 2.5- 4. 5 '30 6. 3 19. 7 D0.

Satisfactory tin-antimony-copper alloys, and in par? ticular thosealloys containing aflpreponderance of tin,

can be electrodedeposited with the fluoborate bath and process of thisinvention. By the close control of the bath composition, currentdensity; circulation, anode material and the conditions enumerated,excellent'deposits of several thousandths and even of several hundredthsof an inch thick can be obtained with close control over the exactcomposition of the deposit. The process and bath of this invention makepossible the electrodeposition of smooth dense deposits of varyingthicknesses whichadhere to metal bases such as steel and other ferrousmetals," copper, copper lead alloys, silver, nickel and other metals andalloys.

Various changes and modifications of the embodiments of the inventiondescribed herein may be made by those skilled in the art withoutdeparting from the spirit and principles of the invention.

I claim:

1. The process of electroplating an alloy containing from about 2 to 12%antimony, from about 1 to 8% copper and the balance tin which consistsin electrodepositing the alloy from an aqueous-bath containing from 50to 180 g./l. tin as tin fluoborate, from .5 to g./l. antimony asantimony fluoborate, from .5 to 20 g./l. copper as copper fluoborate,from 10 to 40 g./l. boric acid, and sufiicient fluoboric acid to.maintain the pH of said bath at less than 1, the current density beingfrom 10 to 60 amperes per square foot.

2. A process in accordance with claim 1 inwhich the anode material isselected from a group consisting of pure tin and the tincopper alloyspredominantly of tin.

3. A process in accordance with claim 1 in which the bath contains from.25 to 2 g./l. glue and about 1 g./l. betanaphthol.

4. An aqueous bath for the electrodeposition of an alloy containing fromabout 2 to 12% antimony, from about 1 to 8% copper and the balance tin,saidbath to 20 g./l. copper as copper fluoborate, from .25 to 2 g./l.glue, from 10 to 40 g./l. boric acid, about 1 g./l. betanaphthol andsufiicient fluoboric acid to maintainthe pH of said bath below 1.

5. -A process for electrodepositing a ternary alloy containing fromabout 2 to 12% antimony, from about 1 to 8% copper and the balance tinconsisting of passing a current suflicient to yield a current density offrom 10 to amperes per square foot between a cathode and an anode andthrough a bath containing from about 60 to g./l. tin as tin fluoborate,from about 1 to 5 g./l. antimony as antimony fluoborate, from about 1 to5 g./l. copper as copper fluoborate, from about 15 to 25 g./l. boricacid, and sufficient fluoboric acid to maintain the pH of said bath atbelow 1.

6'. A process in accordance with claim 5 in which the bath contains from.25 to 2 g./l. glue, and is saturated with betanaphthol.

7. A process in accordance with claim 5 in which the anode material isselected from a group consisting of pure tin and tin-copper alloyspredominantly of tin.

8. An aqueous bath for the electrodeposition of an alloy containing fromabout 2 to 12% antimony, from about 1 to 8% copper and the balance tin,said bath containing from 50 to g./l. tin as tin fluoborate, from .5 to20 g./1. antimony as a compound selected from the group consisting ofantimony fluoborate, antimony trioxide, antimony trifluoride andpotassium antimony tartrate, from .5 to 20 g./1. copper as copperfluoborate, from 10 to 40 g./l. boric acid and sufiicient fluoboric acidto maintain the pH of said bath below 1.

References Cited in the file of this patent UNITED STATES PATENTS2,455,554 Brown Dec. 7, 1948 2,458,827 Booe Jan. 11, 1949 2,523,160Struyk et a1. Sept. 19,1950

8. AN AQUEOUS BATH FOR THE ELECTRODEPOSITION OF AN ALLOY CONTAINING FROMABOUT 2 TO 12% ANTIMONY, FROM ABOUT 1 TO 8% COPPER AND THE BALANCE TIN,SAID BATH CONTAINING FROM 50 TO 180 G./L. TIN AS TIN FLUOBORATE, FROM 5TO 20 G./L. ANTIMONY AS A COMPOUND SELECTED FROM THE GROUP CONSISTING OFANITIMONY FLUOBORATE, ANTIMONY TRIOXIDE, ANTIMONY TRIFLUORIDE ANDPOTASSIUM ANTIMONY TARTRATE, FROM .5 TO 20 G./L. COPPER AS COPPERFLUOBORATE, FROM 10 TO 40 G./L. BORIC ACID AND SUFFICIENT FLUOBORIC ACIDTO MAINTAIN THE PH OF SAID BATH BELOW L.